1. Field of the Invention
The present invention relates to thermal transfer color printers, and more particularly to a thermal transfer color printer for forming multicolor images by thermally transferring inks of different colors from an ink ribbon to recording paper a plurality of times.
2. Description of Related Art
Thermal transfer color printers are already known which are adapted for use with plain paper having specified surface smoothness and serving as a recording medium for transferring a sublimable dye or ink to the paper by a thermal head with application of pressure and heat. Such thermal transfer color printers are used also for producing color images.
These thermal transfer color printers include those adapted to produce color images by repeatedly transferring usually yellow, magenta and cyan inks in succession for each image to be eventually produced. (This type of printers will hereinafer be referred to as the "successive color transfer type.")
Generally in such thermal transfer color printers, recording paper is transported using a platen roller drivingly rotatable in forward and reverse directions as a standard for determining the amount of reciprocating transport of the paper. Various systems for transporting recording paper are also known which include, for example, a system wherein a tractor feeder is used for transporting fanfold paper serving as recording paper in combination with the platen roller as transport means.
However, these conventional thermal transfer color printers have the following problems. To ensure the intimate contact of the thermal head with the platen roller, the platen roller is made of an elastic material such as elastic rubber and is therefore difficult to form accurately in shape. The platen roller deforms on expansion due to the heat transferred from the thermal head. The platen roller as held out of transfer operation, i.e., out of contact with the thermal head, also deforms when brought into thermal transfer operation in pressing contact with the thermal head. If the platen roller is used as the standard for determining the amount of transport of the recording paper, a difference occurs between the amount of forward transport of the paper and that of reverse transport, with the result that the images of different colors which are thermally transferred onto the recording paper individually will not be in accurate register. The misregister of the transferred images (misregister of color impressions) gives rise to a problem in respect of the quality of copy images.
On the other hand, recording paper transport systems wherein different transport means are used as standards for forward and reverse directions are low in the accuracy of transport when reciprocatingly transporting the recording paper repeatedly. The poor accuracy, i.e., a difference between the amounts of forward and reverse transport, similarly poses a problem in respect of the quality of copy images since the images of different colors individually transferred onto the recording paper are out of register (misregister of colors).